Mineralogical and microstructural investigation of lime-treated expansive clay soil from Mosul City, Northern Iraq

This study used an optimum lime content of 4% to stabilize highly expansive soil from Mosul city-Iraq. By applying different curing periods at the extreme temperature of Mosul city, 40°C, the mechanism of soil stabilization was verified through a series of microlevel tests: X-ray diffraction (XRD), thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results revealed significant changes in the structure and mineral constituents of the lime-treated samples due to both short-term and long-term reactions. XRD analysis revealed the production of cementitious compounds, calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), in the early curing period. Throughout the curing periods, XRD revealed an increase in the calcite concentration in the treated samples. The results from the TGA confirmed the creation of cementitious compounds and calcite minerals in the treated samples. The MIP analysis of the natural soil samples revealed a variety of pore size distributions, encompassing both intraaggregate and interaggregate pores. During the early curing periods, the connected porosities of the treated samples increased but then decreased with increasing curing period. In total, the observations from the SEM images matched the overall findings. The deep microlevel analyses provide a logical explanation for the substantial increase in the strength of the treated samples. This study emphasized the importance of high curing temperatures in the prompt initiation of pozzolanic reactions. Compared with the natural soil samples, during the early curing period, the treated samples demonstrated a 5.50-fold increase in unconfined compressive strength. and reached approximately 7.75 times during the later curing period. The findings of the present investigation might augment the limited literature concerning the mineralogical and microstructural alterations of highly expansive soils subjected to elevated temperature conditions.